Amorphous (non-crystalline) oxide semiconductors have high carrier mobility and a high optical bandgap and can be formed at a low temperature compared with widely used amorphous silicon (a-Si), and thus are expected to be applied to next-generation displays which are required to be large, have high resolution, and be operated at high speed, resin substrates having low heat resistance, and the like.
Among oxide semiconductors, in particular, amorphous oxide semiconductors composed of indium, gallium, zinc, and oxygen (In—Ga—Zn—O, hereinafter, may be referred to as “IGZO”) have very high carrier mobility, and therefore, are favorably used. For example, Non-Patent Literatures 1 and 2 each disclose an example in which an oxide semiconductor thin film containing In, Ga, and Zn at a ratio of 1.1:1.1:0.9 (at %) is used as a semiconductor layer (active layer) in a thin film transistor (TFT). Furthermore, Patent Literature 1 discloses an amorphous oxide which contains elements, such as In, Zn, Sn, and Ga, and Mo and in which the atomic composition ratio of Mo to the number of total metal atoms in the amorphous oxide is 0.1 to 5 at %, and discloses in an example thereof a TFT including an active layer in which Mo is added to IGZO.